It has been greatly desired to shorten the time required for development of light-sensitive materials. In order to meet these requirements, the development time has been reduced by raising the development temperature to about 27.degree. C. or higher. This is realized by the use of an automatic developing machine as described in, e.g., Rodal Technol., Vol. 44, No. 4, pp. 257-261 (1973), U.S. Pat. Nos. 3,025,779 and 3,672,288 which permits rapid and highly reproducible development. Such automatic developing machines usually contain a developing tank, a stopping tank, a fixing tank, a water-washing tank, a drying zone, and so forth, and the speed of conveyance of films and the processing temperature can be controlled.
It is known, as described in Furnell et al., J. Photo. Sci., Vol. 18, p. 94 (1970), that with photographic light-sensitive materials using a silver halide emulsion, when the degree of swelling of the material in a developer is changed by changing the degree of hardening of a binder, e.g., gelatin, the covering power based on developed silver can be increased. It has been observed that as the degree of hardening of a silver halide emulsion layer is decreased by reducing the amount of a hardener used, the covering power is further increased.
However, when the degree of hardening is lowered to great extent, the strength of the emulsion layer is seriously reduced, presenting various problems. For example, when processed in an automatic developing machine as described hereinbefore, the emulsion layer is liable to peel apart from the support, or it may be readily scratched during the handling. Furthermore, binders may come out of the light-sensitive materials into the processing liquids in the automatic developing machine. These binders may combine together with each other, or with different compounds from the light-sensitive material in the processing liquid, and form precipitates insoluble in the processing liquid. These insoluble precipitates in the processing liquids are generally called "scum" in the art.
When scum is formed in a processing liquid, it sticks to a light-sensitive material which later passes through the automatic developing machine, causing contamination of the light-sensitive material. The scum sticking to the light-sensitive material seriously deteriorates the image quality of the light-sensitive material, as a result of which the product value is completely lost.
In order to overcome such problems, it is necessary to increase the degree of hardening of a silver halide emulsion layer to some extent. However, this inevitably leads to a reduction in the covering power. Although a number of methods for hardening silver halide emulsion layers are known, none of these methods make it possible to increase covering power without causing the formation of scum in processing liquids.
As a result of extensive studies to solve the above-described problems, it has been found that by controlling the degree of hardening of the uppermost layer independently from those of other underlying layers, i.e., by making the former greater than the latter, the elution of gelatin can be prevented. Accordingly, the formation of scum can be greatly reduced. Although it is well known that unreacted gelatin which has not been cross-linked by a hardener comes out from a light-sensitive material, and that the amount of the unreacted gelatin depends on the degree of hardening, it has been found for the first time according to the present invention that when the degree of hardening of the uppermost layer is increased, even if the degrees of hardening of underlying layers are small, i.e., the proportion of cross-linked gelatin in each of the underlying layers is small, the amount of gelatin eluted can be greatly reduced compared with conventional light-sensitive materials in which the degree of hardening of gelatin is the same in all coating layers. Furthermore, astonishingly, it has been found that the amount of gelatin eluted is based almost totally on the degree of hardening of the uppermost layer and is less affected by the degrees of hardening of the other underlying layers. This indicates that the cross-linking of the uppermost layer produces synergistic effects in the prevention of elution of gelatin. These synergistic effects could not have been anticipated by prior art teachings.